The architecture of an LTE system is shown in FIG. 1. In LTE, the downlink is based on orthogonal frequency division multiplexing (OFDM) while the uplink is based on a single carrier modulation method known as discrete Fourier transform spread OFDM (DFT-S-OFDM)
Some Radio Access Technologies (RATs), e.g., E-UTRAN and UTRAN, support dynamic scheduling of uplink (UL) and/or downlink (DL) data, where radio resources are assigned to users and radio bearers according to the users momentary traffic demand, QoS requirements, and estimated channel quality. The eNB may assign radio resources in time or frequency to UEs experiencing, e.g., higher channel quality than other UEs which compete for the same radio resources.
An example of the radio resources in E-UTRAN are shown in FIG. 2. The smallest entity is a resource element 202. In E-UTRAN, the smallest schedulable entity is called a Scheduling Block (SB), consisting of two consecutive Resource Blocks (RBs), with a total length of 1 ms and width, 208, of 180 kHz, i.e. 12 sub-bands (or subcarriers) of 15 kHz each. An eNB in E-UTRAN allocates SBs to UEs both in time and frequency. In E-UTRAN, a UE may be configured to report Channel Quality Indicator (CQI) reports, indicating the quality of the DL. The scheduler may then assign SBs to the UE based on the CQI reports and QoS requirements.
In a so-called one reuse system, such as LTE, network nodes, e.g. eNBs, serving a respective cell allocate physical radio resource(s), such as a number of Physical Resource Blocks (PRBs) or sub bands, to the UEs in the served cell. When UEs in two neighboring cells are allocated or assigned radio resources which coincide in time and frequency, the transmissions in these radio resources may interfere with each other. Such interference is called a conflict or collision, and is illustrated in FIG. 3. A collision may result in a lower SINR, and one or more HARQ retransmissions may be needed to successfully decode the transmitted bits. Such retransmissions reduce the user throughput.
To alleviate the impact of such collisions and improve the system performance, Inter-Cell Interference Coordination (ICIC) techniques have been proposed. For example, 3GPP has specified a load indication procedure for ICIC, involving X2 signaling between the eNBs to exchange load information.
The load indication procedure for ICIC, specified by 3GPP, includes two load indicators:                The Interference Overload Indicator (IOI).                    The IOI indicates the interference level experienced by the indicating cell on all resource blocks. The IOI message indicates, per PRB, whether the PRB is subjected to high, medium or low interference.                        The High Interference Indicator (HII).                    The HII indicates the occurrence of high interference sensitivity, as seen from a transmitting eNB. The message is a bit map indicating high or low interference sensitivity per PRB.                        
FIG. 4 shows an example scenario, where an IOI is transmitted from a cell A to a cell B over the X2 interface. The IOI indicates high interference for ⅓ of the PRBs (at the higher frequencies of the frequency bandwidth). The IOI further indicates low interference for the remaining ⅔ of the PRBs in question. Having received the IOI message, the receiving cell, cell B as shown in FIG. 4, may take the IOI information into account when scheduling radio resources, and select e.g. UEs located at the cell-center to be scheduled on PRBs indicated as subjected to high interference, in order to reduce interference to the indicating cell, i.e. cell A in this example.
FIG. 4 also shows a HII indicator being transmitted from cell A to cell B over the X2 interface. The HII indicates high interference sensitivity for ⅔ of the PRBs (at the lower frequencies of the frequency bandwidth) concerned by the HII. The HII further indicates low interference sensitivity for the remaining ⅓ of the PRBs in question. Having received a HII message, the receiving cell, cell B in this example, may take the HII information into account when scheduling radio resources, and e.g. avoid scheduling cell-edge UEs on the PRBs indicated as having a high interference sensitivity. The cell-edge UEs may be scheduled at the remaining ⅓ of the PRBs where interference sensitivity is low.
It could be questioned how a serving node in a cell (e.g. cell A in the example above) can know that it is users in a certain neighbor cell, e.g. cell B, that are causing interference to cell A. In the load indication procedure specified by 3GPP, it is assumed that the serving node has support from UE measurements, providing information about the vicinity. Further, a serving node in cell B can compare, e.g. the information in an IOI message from cell A, with what in fact was transmitted in cell B during the PRBs in question. This also implies the possibility that cell A may send IOI to more than one potentially interfering cell, e.g. when it is not obvious which the main interferer is.